Stock-Based Compensation (Details 3) (USD $) In Thousands, except Per Share data, unless otherwise specified	9 Months Ended
	Sep. 30, 2012
Number of shares
Outstanding at the beginning of the period (in shares)	17,617
Granted (in shares)	3,220
Exercised (in shares)	(857)
Forfeited (in shares)	(168)
Outstanding at the end of the period (in shares)	19,812
Exercisable at the end of the period (in shares)	14,692
Vested and expected to vest at the end of the period (in shares)	19,414
Weighted average exercise price
Outstanding at the beginning of the period (in dollars per share)	$ 2.56
Granted (in dollars per share)	$ 7.46
Exercised (in dollars per share)	$ 2.17
Forfeited (in dollars per share)	$ 4.23
Outstanding at the end of the period (in dollars per share)	$ 3.34
Exercisable at the end of the period (in dollars per share)	$ 2.32
Vested and expected to vest at the end of the period (in dollars per share)	$ 3.29
Aggregate intrinsic value
Outstanding at the beginning of the period (in dollars)	$ 74,329
Outstanding at the end of the period (in dollars)	119,270
Exercisable at the end of the period (in dollars)	103,676
Vested and expected to vest at the end of the period (in dollars)	$ 118,313